[gcc(refs/vendors/ibm/heads/gcc-9-branch)] aarch64: ensure bti c is emitted at function start [PR94697]

[Peter Bergner]

https://gcc.gnu.org/g:f6e42cdee5de2b3441afc88c8888c1166bdffe57

commit f6e42cdee5de2b3441afc88c8888c1166bdffe57
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Fri Apr 17 16:54:12 2020 +0100

    aarch64: ensure bti c is emitted at function start [PR94697]
    
    The bti pass currently first emits bti c at function start
    if there is no paciasp (which also acts as indirect call
    landing pad), then bti j is emitted at jump labels, however
    if there is a label right before paciasp then the function
    start can end up like
    
      foo:
      label:
        bti j
        paciasp
        ...
    
    This patch is a minimal fix that just moves the bti c handling
    after the bti j handling so we end up with
    
      foo:
        bti c
      label:
        bti j
        paciasp
        ...
    
    This could be improved by emitting bti jc in this case, or by
    detecting that the label is not in fact an indirect jump target
    and then this situation would be much less common.
    
    Needs to be backported to gcc-9 branch.
    
    Backported without the testcase because of missing infrastructure
    for check-function-bodies.
    
    gcc/ChangeLog:
    
            Backport from mainline.
            2020-04-23  Szabolcs Nagy  <szabolcs.nagy@arm.com>
    
            PR target/94697
            * config/aarch64/aarch64-bti-insert.c (rest_of_insert_bti): Swap
            bti c and bti j handling.

Diff:
---
 gcc/ChangeLog                           |  9 +++++++++
 gcc/config/aarch64/aarch64-bti-insert.c | 32 ++++++++++++++++----------------
 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b36c9d53d26..1b814c7308b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2020-05-14  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	Backport from mainline.
+	2020-04-23  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	PR target/94697
+	* config/aarch64/aarch64-bti-insert.c (rest_of_insert_bti): Swap
+	bti c and bti j handling.
+
 2020-05-14  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	Backport from mainline.
diff --git a/gcc/config/aarch64/aarch64-bti-insert.c b/gcc/config/aarch64/aarch64-bti-insert.c
index e519a0f0ac1..9e0fc168435 100644
--- a/gcc/config/aarch64/aarch64-bti-insert.c
+++ b/gcc/config/aarch64/aarch64-bti-insert.c
@@ -130,22 +130,6 @@ rest_of_insert_bti (void)
   rtx_insn *insn;
   basic_block bb;
 
-  /* Since a Branch Target Exception can only be triggered by an indirect call,
-     we exempt function that are only called directly.  We also exempt
-     functions that are already protected by Return Address Signing (PACIASP/
-     PACIBSP).  For all other cases insert a BTI C at the beginning of the
-     function.  */
-  if (!cgraph_node::get (cfun->decl)->only_called_directly_p ())
-    {
-      bb = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb;
-      insn = BB_HEAD (bb);
-      if (!aarch64_pac_insn_p (get_first_nonnote_insn ()))
-	{
-	  bti_insn = gen_bti_c ();
-	  emit_insn_before (bti_insn, insn);
-	}
-    }
-
   bb = 0;
   FOR_EACH_BB_FN (bb, cfun)
     {
@@ -201,6 +185,22 @@ rest_of_insert_bti (void)
 	}
     }
 
+  /* Since a Branch Target Exception can only be triggered by an indirect call,
+     we exempt function that are only called directly.  We also exempt
+     functions that are already protected by Return Address Signing (PACIASP/
+     PACIBSP).  For all other cases insert a BTI C at the beginning of the
+     function.  */
+  if (!cgraph_node::get (cfun->decl)->only_called_directly_p ())
+    {
+      bb = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb;
+      insn = BB_HEAD (bb);
+      if (!aarch64_pac_insn_p (get_first_nonnote_insn ()))
+	{
+	  bti_insn = gen_bti_c ();
+	  emit_insn_before (bti_insn, insn);
+	}
+    }
+
   timevar_pop (TV_MACH_DEP);
   return 0;
 }